


Day Sixteen

by FellQueen (Nikasha)



Series: Kinktober 2019 [16]
Category: Undertale (Video Game)
Genre: Fisting, M/M, Sibling Incest, Underfell Papyrus (Undertale), Underfell Sans (Undertale), Vaginal Fisting
Language: English
Status: Completed
Published: 2019-10-18
Updated: 2019-10-18
Packaged: 2020-12-22 18:03:54
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 1,297
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/21080792
Author URL: https://archiveofourown.org/users/Nikasha/pseuds/FellQueen
Summary: Day SixteenPrompt: FistingPairing: Fellcest (Underfell!Papyrus/Underfell!Sans)





	Day Sixteen

**Author's Note:**

> I’m behind, my bad. I do have Day 17 ready too, I’ll post it later.

Sans was shaking. He had both hands pressed over his mouth and his teeth were digging into his fingers, drawing blood. He kept his gaze on Papyrus between his legs, red eyelights hazy with lust.  
He was already dripping wet. Papyrus had two fingers knuckle-deep in his cunt and Sans felt like they reached into his belly. They were so _long._ The taller skeleton crooked his fingers and Sans let out a muffled, strangled sound as he flinched.  
“Brother, this is really all it takes to bring you down?” Papyrus purred, voice low. He filled it with disgust that made Sans whine. “Pathetic.”  
Sans opened his mouth, but quickly chomped down on his hand again when Papyrus slid a third digit into him. His fingers were going to be a mangled mess at this rate. He swallowed a couple times and cleared his throat before managing, “What’s pathetic is how carefully you’re handling me. I ain’t gonna break if you go a little crazy, boss.” He almost didn’t sound like he had been choking on dick. The sad part was that he hadn’t been.  
Papyrus chuckled darkly. “Oh, Sans, you overestimate yourself. But very well.” He added a fourth finger and started spreading them wide. When Sans choked, Papyrus reached out and grabbed his wrist, keeping him from putting his hand back over his mouth. “I want to hear you.”  
Sans brushed the side of his skull with his shoulder, trying to wipe away some of the sweat. “You want people to know we’re vulnerable?” he said dubiously.  
Papyrus smiled, all teeth and sharp points. “I would enjoy seeing those bastards try to hurt us.” He sounded amused.  
Sans went to retort, but just broke into a loud cry when Papyrus spread his fingers again. His free hand clawed at the sheets, the one Papyrus held gripping his brother’s wrist tightly. “Fuck, Boss,” he wheezed. “I don’t think your fist is that wide.”  
“Oh, hush.” Papyrus turned and bit the femur resting on his shoulder, making Sans squirm. When he let go, magic welled from the teeth marks.  
“Fuck,” Sans said again, almost impressed by the bite. If he sat down, his shorts probably wouldn’t cover it.  
“Mine,” Papyrus said sweetly. He curled his thumb inward and began to press.  
Sans stiffened briefly before forcing himself to go loose. He reached down to finger his clit and that helped, focusing on the little shocks of pleasure rather than the overwhelming pressure beginning to spread through his pelvis. He couldn’t entirely ignore it, though, that was impossible. He hissed as a sharp pain lanced through him and Papyrus halted.  
“Sans,” he said sternly, gaze piercing. It felt like red spotlights on his very soul.  
Sans noticed Papyrus had gripped his hand a bit tighter.  
He panted and gave a small shake of his head. “I’m fine, I’m fine,” he said. “Just caught me off-guard.”  
Despite his reassurances, Papyrus didn’t move. He let go of Sans’s hand, giving him the slightest pang of disappointment that he quickly axe-murdered, and gripped his spine, sharp fingers digging between the vertebrae. Sans yelped and moaned, his magic searing its way to his spine to protect him.  
While he was distracted, Papyrus resumed pushing inwards. The widest part of his hand caught against the outside of his cunt and Sans made a sound like he had been kicked. Papyrus glanced at him but persisted.  
A slick glide, a strange feeling of release, and Sans’s pussy closed around Papyrus’s wrist.  
Sans huffed in breaths, making little grunts of noise. He squeezed around Papyrus’s hand and moaned. His brother echoed the noise, resting a hand on Sans’s hip and trying his best not to move. Luckily, Papyrus’s best was pretty damn good.  
“So much,” Sans blurted out. “Oh stars, Paps, oh fuck.” It was the wrong name, but he didn’t care. It felt so wrong and so right, and he wanted more. More of his hand, but mostly more of Papyrus himself. The Great, the Ruthless, and the one and only monster Sans would ever let himself love.  
Papyrus made a noise and the vulnerability in it was like a punch. Sans quickly opened his eyes to look at him and was faced with a look of such tender longing and pride that he balked. No, Papyrus couldn’t get attached. Not to the 1hp asshole who couldn’t keep him safe.  
Sans squeezed again, ignoring the ache, and glared. “You gonna fuck me or what?” he challenged.  
The soft look was gone like it had never been. Papyrus grinned and chuckled. “Oh brother. You never learn.”  
He closed his hand and pushed in until he couldn’t anymore, Sans arching his back and scrabbling helplessly at the blankets. He wanted to kick or close his legs, but one was on Papyrus’s shoulder still and the other down by his hip. He was spread open and exposed. He realized he was moaning like a desperate little bitch and stopped, gasping for air he didn’t really need.  
Papyrus had a look on his face that Sans couldn’t quite place. It wasn’t tender, but it wasn’t quite his usual harshness. Something like desire. Possessiveness, maybe.  
Even as he put a finger on the emotion on the other’s face, Papyrus withdrew his hand and began to slowly fuck Sans with it. Any stray thought was shoved straight out of his skull by it until nothing was left but heat and wet and Papyrus’s fist deep in his cunt. His knuckles scraped against Sans’s walls and the friction made him shudder and writhe like he was going to escape.  
He didn’t remember cumming. Everything was hazy and unfocused like he was drunk or high. But he had to have, because the noises Papyrus’s hand were making in his body suddenly seemed much louder, and the agonizing stabs of euphoria almost too much. “B-oss,” he begged, feeling returning to him slowly. He could see his legs trembling around Papyrus. His entirely body shook.  
“Good,” Papyrus said firmly, but quietly. Throwaway praise almost, but coming from Papyrus, it had Sans preening tiredly. An awful sound was wrenched from deep inside him when Papyrus pinned his spine and slowly pulled out his hand. Sans felt so...empty. He was pretty sure he was stretched wide, a faint ache in his pussy. He dismissed the magic and the ache diffused throughout his pelvis.  
Papyrus drew a deep crimson tongue over his hand. It was drenched like he had put it under a faucet. He noticed Sans looking and gave him a sultry stare.  
Sans swallowed, ignoring the soft throb in his magic. Anymore screwing around would have him unable to act quickly enough if need be, and he wouldn’t stand for that.  
Papyrus flicked his hand negligently, ridding it of excess slick, then moved Sans’s leg off his shoulder. He laid behind him, wet hand draped across his hip.  
Sans shivered and wrinkled his nasal bridge but didn’t rebuke that, this time. He noticed a ridiculously hard bump pressed into his tailbone. “C’n give you a blowjob in a few,” he offered. “Or just grind it out on my ass.”  
Papyrus huffed, amused and irritated. “Of course you would say that. I shall take care of it, do not worry, but for now, rest. You keep making strange noises in your throat.”  
Sans tried not to make his horror obvious. He was trying to purr. Great stars, he was so out of it, he had been trying to purr.  
It was almost more horrifying that Papyrus didn’t know what it was. It left a deep pain in his soul like it was going to break.  
Well, maybe it was better this way. Sans slipped into the void of unconsciousness, his brother at his back to guard.

**Author's Note:**

> List used: https://twitter.com/idek_uggy/status/1178349575725174786?s=21
> 
> Next is gags


End file.
